CN1654999A - Multiple order pmd compensator for optical fiber transmission system - Google Patents

Abstract

System for managing radiographic images includes a capture device, a file server, a database server, a user workstation, and a data storage device with removable media. Digital images are captured by the capture device, automatically stored on the file server, maintained as the original image and archived to the data storage device. The workstation copies and displays digital images. The database server includes image records and patient records. The image records include all user manipulations of the digital image as commands, and recalled digital images are displayed as last viewed.

Description

The multi-order polarization module color dispersion compensator that is used for fibre-optic transmission system (FOTS)

Technical field

The present invention relates to fibre-optic transmission system (FOTS), particularly a kind of transmission system with a compensator, this compensator is used to reduce the multistage influence of polarization mode dispersion.

Background technology

Fibre-optic transmission system (FOTS) is beginning to realize its great potential of transmission bulk information fast.In essence, optical transmission system is made up of an optical signal source and an Optical Fiber Transmission path, and this path is used for optical signal transmission to is used to make the receiver of the entrained demodulates information of signal.More and more, light signal is the wavelength-division multiplex signals (WDM or DWDM signal) that comprises a plurality of different wavelength channels.In each channel, information is transmitted with the form of an optical pulse sequence typically.

Polarization mode dispersion compensator is the element that has potential importance in the optical transmission system.When the different orthogonal polarized component of a signal had different propagation delays, polarization mode dispersion (PMD) will produce.The different delays that optical fiber and the flaw in the optical element can produce polarized component.These different delays can make the shape distortion of transmission light pulse.

PMD is in the higher bit transfer rate, particularly in 40Gb/s or the higher transfer rate, and the problem that more and more receives publicity.In addition, because PMD can change along with frequency, compensate also more and more difficult to the system of transmitting optical signal in wide frequency range.Therefore, having the fibre-optic transmission system (FOTS) that has improved the PMD compensation is the ten minutes needs.

Summary of the invention

According to the present invention, provide a kind of fibre-optic transmission system (FOTS), in the scope of a frequency change in order under high bit rate and the compensation of enhancing is provided with multistage PMD compensation.Especially, the assembly compensation that PMD is got up by a succession of link, each assembly is provided with in order to compensate the higher in succession rank item of PMD Taylor series approximation value.More preferably, each assembly comprises the disperisivity quotient element of a Polarization Controller and a specific rank item.In an example, single order disperisivity quotient element can be differential group delay (DGD) element of a standard.Second order element can be a differential group velocity dispersion element, and three rank elements can be disperisivity quotient slope element.In different embodiment, the disperisivity quotient element of these various exponent numbers can be an element that fix or tunable.

Description of drawings

In conjunction with the accompanying drawings, the illustrative embodiment that will describe in detail below considering, can more be expressly understood advantage of the present invention, essence and various additional feature.In the accompanying drawings:

Fig. 1 is for showing the synoptic diagram of the fibre-optic transmission system (FOTS) that includes a multistage PMD compensator;

Fig. 2 is for describing the synoptic diagram of a typical multistage compensator that is used for Fig. 1 embodiment in detail;

Fig. 3 is for describing the synoptic diagram of an alternative typical second order PMD compensating element, that is used for Fig. 1 embodiment in detail;

Fig. 4 is a synoptic diagram of describing another selectable typical second order PMD compensating element, of the embodiment that is used for Fig. 1 in detail; And

Fig. 5-10 is for being used to explain principle of the present invention and theoretical synoptic diagram.

Be appreciated that these figure are in order to explain content of the present invention, and except chart, these figure draw in proportion.

Embodiment

This description is divided into two parts, and part i is described illustrative examples of the present invention, and part ii is described principle of the present invention and extension on its basis in detail to those of ordinary skill in the art.

I. the optical transmission system that has multistage PMD compensation

With reference to accompanying drawing, Fig. 1 illustrates to have described a fibre-optic transmission system (FOTS) 10, this system comprises an information carrier light-pulse generator 11, one transmission channel 12, form the optical receiver 14 that a multistage PMD compensator 13, can freely be selected by the optical fiber that is used to transmit from the light signal of light source 11, with the monitor that can freely select 15, monitor 15 is used for a feedback signal 16 is offered multistage PMD compensator 13.Suppose that optical fibre channel 12 has undesired polarization mode dispersion.Signal source 11, optical fibre channel 12, receiver 14 and monitor 15 can be existing, the well-known conventional equipment in this area.

Multistage PMD compensator 13 comprises a plurality of compensation assembly A, B, and C ..., each compensation assembly is used for compensating the rank item that one after the other increases successively at the PMD taylor series expansion about wavelength.As what proved in the second portion, the PMD as the angular frequency function can be expressed as the Taylor series approximation value.According to the present invention, compensation assembly A compensates first influence of this progression approximate value, second of B compensation, and C compensates the 3rd.If desired, can provide other assembly to compensate the more influence of higher order term.

Fig. 2 has shown a typical multistage compensator 13 that is used for Fig. 1 system in detail.Assembly A in succession, B, the rank item that the C compensation is one after the other increased in the Taylor series approximation value of PDM vector successively, this PDM vector is certain center carrier frequencies ω ₀The function of frequencies omega on every side.In this Taylor series approximation value, than centre frequency ω ₀The PMD vector at the frequency place of a big frequency increment Δ ω With a sequence rank item and come approximately, we consider this approximate in its first three items respectively, that is: 1) at ω ₀The PMD vector at place, 2) at ω ₀The PMD of place vector is with respect to the slope of frequency, 3) at ω ₀Place's slope is with the speed of frequency change.Equally also can use higher rank item.On the mathematics, at ω ₀The PMD vector at place is available

Expression is at ω ₀The slope at place can be used

Expression is at ω ₀The speed of place's slope variation can be used Expression.Therefore, Be ω ₀The PMD vector at place, Be

With respect to the derivative of ω at ω ₀The value at place,

Be With respect to the second derivative of ω at ω ₀The value at place.Utilize this progression approximate value, at ω=ω ₀The PMD vector at+Δ ω place can be approximately:

The present invention imagines the compensation with compensator A

Influence, with compensator B compensation ${\stackrel{\→}{\mathrm{\τ}}}_{\mathrm{\ω}}\left({\mathrm{\ω}}_0\right)\mathrm{\Δ\ω}$ Influence, with compensator C compensation ${\stackrel{\→}{\mathrm{\τ}}}_{\mathrm{\ω\ω}}\left({\mathrm{\ω}}_0\right)\frac{{\mathrm{\Δ\ω}}^2}{2}$ Influence.More high-order term can be ignored usually, but if supplement is repaid, they also can be compensated.

Below, assembly A, B and C will comprise the particular components with chromatic dispersion, when light passed through optics or optical fiber, different frequency (wavelength) can obtain different time delays.Chromatic dispersion is caused to the dependence of frequency by the refractive index of material and waveguide design.Polarization mode dispersion is the degree of dependence of time delay to polarizing by optics or optical fiber.(PMD can to or can frequency not had dependence).Polarization mode dispersion is relevant with chromatic dispersion, the time delay when they have all reflected by optical fiber or optics.

Similar to polarization mode dispersion, the effect of chromatic dispersion can by with mode propagation constant β at carrier frequency ω ₀Near expansion in Taylor series is explained:

Here, we define β _ωBe 1st order chromatic dispersion, perhaps more accurately, be " chromatic dispersion of single order phase velocity " that it has determined group velocity or delay, β _{ω ω}Be 2nd order chromatic dispersion (or group velocity dispersion, perhaps abbreviate chromatic dispersion sometimes as), β _{ω ω ω}Be third-order dispersion (or claiming chromatic dispersion gradient).Hereinafter, the disperisivity quotient on specific rank is with reference to such a case, that is: when by an optical element transmission, the polarization of pairwise orthogonal experiences the different chromatic dispersions of this order.

The first assembly A only need be a routine single order PMD compensator, differential optical delay line for example, at this, the optical delay (1st order chromatic dispersion) that pairwise orthogonal polarization experience is different.The differential delay line can be made of a Polarization Controller 20A, a polarization beam splitter 21A, a delay element 22A and an optical polarization beam combiner 23A.Catoptron 24A and 25A can be with their the suitable paths of beam direction that divided.Polarization Controller 20A rotatory polarization is so that be directed to the path at a slow speed of compensator from the polarized component with fast speed transmission of optical fiber, and enters the quick path of compensator from the polarized component with than the jogging speed transmission of optical fiber.As people such as H.Sunnerud at Journalof Lightwave Technology, volume 20 in 2002, described in the 2204-2219 page or leaf like that, select delay element 22A to make it compensation at center carrier frequencies ω ₀The polarization dispersion at place, or make it the mean value of compensation on expected bandwidth (for example, the bandwidth of signal) People such as F.Heismann have described in further detail the structure and the operation of conventional single order PMD compensator in the Proceedings of the European Conference on OpticalCommunication of 529-530 page or leaf in 1998.One differential optical delay line can postpone to construct equally by settling on two polarization paths, just can as long as optical delay is different.Rolled up 30 as people such as T.Takahashi in 1994, the Electronics Letters of 348-349 page or leaf, as described in, as another selection, a single order PMD compensator also can be connected to the Polarization Controller formation that one section polarization is kept (PM) optical fiber after one.

The second assembly B is a second order PMD compensator, and it is according to the slope of PMD vector entries for frequency PMD is compensated.Except assembly B provides the second-order differential chromatic dispersion, rather than provide outside the differential delay (1st order chromatic dispersion), assembly B can be similar with assembly A.Element 22B includes one or more elements with group velocity dispersion, and for example dispersion compensating fiber or Fiber Bragg Grating FBG are in order to provide the differential GVD (Group Velocity Dispersion) of part B.Shown in Fig. 3 and 4, as selection, disperisivity quotient also can be by providing the GVD (Group Velocity Dispersion) (D of different value respectively on two polarization paths ₁And D ₂) or the GVD (Group Velocity Dispersion) of the identical but opposite in sign of amplitude (+| D| and-| D|) realize.In some cases, in particularly realizing for the technology shown in Fig. 2 and 3, (not relying on polarization) the group velocity dispersion compensator that might increase by one in PMD compensator back, any common, (not relying on polarization) GVD (Group Velocity Dispersion) of adding by the PMD compensator in order to compensation.Please note: the simulation that realizes for the technology of the compactness of components A differential delay seems for part B it also is possible.For example, this technology realizes needing an optical fiber that has different group velocity dispersions for the pairwise orthogonal polarization.

The 3rd compensator C is one three a rank PMD compensator, and it is according at the secondary local derviation of the PMD of carrier frequency vector with respect to frequency

PMD is compensated.Three rank PMD compensators can be similar to part B, have the element 22C that comprises one or more chromatic dispersion gradient elements.Be similar to part B, chromatic dispersion gradient that can be by different value is provided respectively or size is identical but chromatic dispersion gradient opposite in sign provides the disperisivity quotient slope on two polarization paths.And in some cases, for compensate any total, by (with polarization irrelevant) chromatic dispersion gradient that the PMD compensator adds, need after the PMD compensator, increase (with a polarization irrelevant) dispersion slope compensation device.

Multistage compensator 13 can utilize fixing or adjustable differential delay and dispersion element to come the system of compensation image 1.The main polarization state of the same order item by each compensation rank item being regulated each Polarization Controller, can force the polarization state that sends and fiber transmission link and PMD compensator combined system aligns.This method has reduced the quantity of control signal, and does not need adjustable differential delay or chromatic dispersion.If differential delay and dispersion element are adjustable, just can further realize the optimization of PMD compensation.

II. theory and example

Polarization mode dispersion is a transmission attenuation that is caused by fiber birefringence.Little defective that produces in the optical fiber manufacture process and/or the stress that is applied on the optical fiber in the optical cable have caused the random variation of birefringence axis along fiber lengths.For single order item (that is: when signal bandwidth is very little),, exist the differential group delay (DGD) between two orthogonal polarisation state that are called as principal state of polarization (psp) (principal states ofpolarization (PSP)) at fiber-optic output.In the receiver that directly detects, the intensity addition that has collimated with two principal state of polarization (psp) (PSP) has caused broadening and intersymbol interference of pulse together.PMD uses the PMD vector usually $\stackrel{\→}{\mathrm{\τ}}=\mathrm{\Δ\τ}\hat{p}$ Describe, wherein Δ τ is differential group delay (DGD), vector of unit length Get the direction of slower that principal state of polarization (psp) (PSP).For single order PMD, Δ τ and Be assumed to be and on a signal bandwidth, be constant.

In some cases, signal bandwidth Δ ω is than the bandwidth deltaf ω of main attitude _PSPWant big, that is: Δ ω＞Δ ω _PSP=π/(4 Δ τ), wherein Δ τ is the average differential group delay (DGD) of optical fiber, main attitude bandwidth is defined as: on this bandwidth, the PMD vector $\stackrel{\→}{\mathrm{\τ}}=\mathrm{\Δ\τ}\hat{p}$ It reasonably is constant.Then, we need consider the PMD of high-order, and it has described the variation of the differential group delay (DGD) that causes with the change of wavelength because of wavelength and because of the orientation of principal state of polarization (psp) (PSP).Because of the system injury that the polarization mode dispersion of high-order produces much more complicated than simple pulse division.Utilize the PMD vector at carrier frequency ω ₀Near the common expansion of Taylor series, $\stackrel{\→}{\mathrm{\τ}}({\mathrm{\ω}}_0+\mathrm{\Δ\ω})=\stackrel{\→}{\mathrm{\τ}}\left({\mathrm{\ω}}_0\right)+{\stackrel{\→}{\mathrm{\τ}}}_{\mathrm{\ω}}\left({\mathrm{\ω}}_0\right)\mathrm{\Δ\ω}+......,$ So-called second order PMD can be with the derivative with two ${\stackrel{\→}{\mathrm{\τ}}}_{\mathrm{\ω}}=\frac{d\stackrel{\→}{\mathrm{\τ}}}{\mathrm{d\ω}}=\mathrm{\Δ}{\mathrm{\τ}}_{\mathrm{\ω}}\hat{p}+\mathrm{\Δ\τ}{\hat{p}}_{\mathrm{\ω}}$ Describe.In this expression formula, be parallel to single order PMD vector first be differential group delay with wavelength change, it causes the chromatic dispersion relevant with polarization (PCD), has caused pulse compression relevant with polarization and broadening.The variation relevant with polarization takes place CHROMATIC DISPERSION IN FIBER OPTICS is understood.Second Principal state of polarization (psp) (PSP) has been described how with the frequency rotation and be called as the PSP depolarization.The pulse distortion that is caused by the PSP depolarization comprises that the generation of association pulse and jumping increase.The PSP depolarization has injurious effects for single order PMD compensator equally.Research has shown to have complicated interacting between chromatic dispersion, chirp (chirp) and second order PMD.May be because the complicated character of second order PMD, though system upgrade for the 10Gb/s to 40Gb/s of old embedded fiber, the influence of these high-orders is very important, for the work understanding three rank in the optical fiber or more done so far in the influence of the PMD of high-order seldom.

Though the taylor series expansion of PMD vector has defined the single order and the PMD of high-order more,, the simple physics of influence on time domain that does not provide high order PMD explained.Say that more accurately this expansion does not provide a kind of being used for and constructs the method for (frequency dependence) Jones matrix of optical fiber for each PMD of high-order more.H.Kogelnik, L.E.Nelson and J.P.Gordon have proposed the method for a head it off recently at Journal of Lightwave Technology in 2003 on the 482-495 page or leaf of volume 21.For analog optical fiber, we adopt the Jones matrix that has different rotary power on frequency.For second order simulation, as the Electronics Letters volume 35 of people such as Eyal, propose first on the 1658-1659 page or leaf in 1999, two parts of different rotary power are linked together, the Jones matrix that couples together is U=U ₂U ₁Here, U ₁And U ₂Has turning axle respectively with frequency-independent

With With form be ${\mathrm{\&phi;}}_2({\mathrm{\&omega;}}_0+\mathrm{\&Delta;\&omega;})={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="A20041004235200203.png"\; state="\{\{state\}\}">k</figure-callout>}}_1\mathrm{\&Delta;\&omega;}$ And φ ₂(ω ₀+ Δ ω) k ₂Δ ω ²/ 2 the anglec of rotation.The rotation power of each part is represented with the power of Δ ω.The PMD vector of single part is as can be seen ${\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_1\left(\mathrm{\&omega;}\right)={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="A20041004235200203.png"\; state="\{\{state\}\}">k</figure-callout>}}_1{\widehat{\mathrm{\&gamma;}}}_1$ With ${\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_2\left(\mathrm{\&omega;}\right)={\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="A20041004235200203.png"\; state="\{\{state\}\}">k</figure-callout>}}_2{\widehat{\mathrm{\&gamma;}}}_2\mathrm{\&Delta;\&omega;}.$ And, utilize U ₁(ω ₀)=I, U ₂(ω ₀)=I (I is a unit matrix) and PMD vector connects rule, and the PMD vector of outputs place that connect two parts is ${\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_1\left(\mathrm{\&omega;}\right)={\mathrm{<figure-callout\; id="1"\; label="k"\; filenames="A20041004235200203.png"\; state="\{\{state\}\}">k</figure-callout>}}_1{\widehat{\mathrm{\&gamma;}}}_1$ (for the single order item) and ${\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_2\left(\mathrm{\&omega;}\right)={\mathrm{<figure-callout\; id="2"\; label="k"\; filenames="A20041004235200203.png"\; state="\{\{state\}\}">k</figure-callout>}}_2{\widehat{\mathrm{\&gamma;}}}_2$ (for second order term).Please note U ₂U ₁The three rank PMD that connect are non-vanishing, and it relates to the vector product of single order and second order PMD vector.

In people's such as Kogelnik research,, this second order simulation is extended to the rotation of high-order power in order to set up the simulation of high-order PMD influence.Except the anglec of rotation with frequency dependence is φ _n(ω ₀+ Δ ω)=k _nΔ ω ⁿ/ n! , and each rotating element that oneself is all arranged with turning axle frequency-independent Outward, rotating element and the top element U that outlines ₁And U ₂Be similar.We can define a rotating vector ${\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_n=k_n{\widehat{\mathrm{\&gamma;}}}_n,$ It is a Stokes vector of having portrayed n power rotation.Like this, the PMD vector of each rotating part simply becomes: ${\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_n\left(\mathrm{\&omega;}\right)=\mathrm{\&Delta;}{\mathrm{\&omega;}}^{n-1}{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_n/(n-1)!.$

In fact, the advantage of the rotating element that these high powers are inferior is: under carrier frequency (Δ ω=0), they only comprise the PMD of an order, that is to say, they only comprise that the level of a rotation is inferior.In other words, they are pure high-order polarization mode dispersion (PMD) element.For example, under carrier frequency, U ₁Part only comprises single order PMD, and U ₂Part only comprises second order PMD.

Show as people's such as Kogelnik research institute, utilize high order power rotating element and the high-order PMD vector to be connected rule and Stokes vector representation ${\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_n=k_n{\widehat{\mathrm{\&gamma;}}}_n,$ Recently, constructed simulation for the polarization mode dispersion (PMD) of optical fiber until quadravalence and six rank.For example, Fig. 5 shows the connection of four elements to build the simulation until quadravalence polarization mode dispersion (PMD).(note that U ₀The Polarization Controller of expression one and frequency-independent.)

An important aspect that utilizes the inferior rotating element of these high powers to set up the simulation of PMD is that these elements physically can be realized.Each element is the disperisivity quotient of a specific order.For example, U ₁The disperisivity quotient of expression single order item, i.e. differential group delay (DGD), U ₂Expression differential GVD (Group Velocity Dispersion), and U ₃Then represent slope of disperisivity quotient or the like.

What the present invention here was concerned about is to utilize above-described high power time rotating element compensation high-order polarization mode dispersion.Because PMD can simulate (or emulation) with the inferior rotating element of these high powers, same available these elements of this PMD compensate.Influence until the PMD of a specific order is by utilizing fixing or adjustable disperisivity quotient element to compensate.

For example, if the polarization mode dispersion (PMD) of known (optical fiber, system, or the like) that will be compensated be until three rank items be, (that is: $\stackrel{\&RightArrow;}{\mathrm{\&tau;}}\left({\mathrm{\&omega;}}_0\right),{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_{\mathrm{\&omega;}}\left({\mathrm{\&omega;}}_0\right),{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_{\mathrm{\&omega;\&omega;}}\left({\mathrm{\&omega;}}_0\right)$ Be known), optical fiber can be by the inferior swing element simulation of high power shown in Figure 6, and wherein subscript i represents to rotate order.The front shows: ${\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_1=\stackrel{\&RightArrow;}{\mathrm{\&tau;}}\left({\mathrm{\&omega;}}_0\right),{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_2={\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_{\mathrm{\&omega;}}\left({\mathrm{\&omega;}}_0\right),{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_3={\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_{\mathrm{\&omega;\&omega;}}\left({\mathrm{\&omega;}}_0\right)+\stackrel{\&RightArrow;}{\mathrm{\&tau;}}\left({\mathrm{\&omega;}}_0\right)\&times;{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_{\mathrm{\&omega;}}\left({\mathrm{\&omega;}}_0\right),$ Yet Be one with the curl of frequency-independent, and must do not compensated by quilt.Then, as shown in Figure 7, we can place one by high power time swing element behind optical fiber The compensator that constitutes.

Be used for the polarization mode dispersion of bucking-out system in order to find out

With

Value, we utilize following equation, in the above in the chart from the output of compensator backward to Input all six part links are got up (we because do not need the compensated optical fiber polarization state, by

The rotation of any and frequency-independent of expression).

For single order PMD: ${\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s={\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_{\mathrm{sn}}+R_n^T{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s(n-1)$

For second order PMD: ${{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;}={{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_{\mathrm{sn}}}^{\&prime;}+{R_n^T}^{\&prime;}{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s(n-1)+R_n^T{{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;}(n-1)$

For three rank PMD: ${{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;\&prime;}={{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_{\mathrm{sn}}}^{\&prime;\&prime;}+{R_n^T}^{\&prime;\&prime;}{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s(n-1)+{{2R}_n^T}^{\&prime;}{{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;}(n-1)+R_n^T{{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;\&prime;}(n-1)$

(represent differential with symbol ' (primes) rather than subscript ω here.In fact subscript T on the R matrix should be " dagger number " of an expression conjugater transformation)

Fig. 8 is a R ^TDerivative table.It is listed at carrier frequency ω to utilize these to connect among rules and Fig. 8 ₀The place is for the R of different rotary degree ^TDerivative, we can carry out one by one iteration towards optic fibre input end, obtain different piece all PMD vectors and.

Input:

${\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s={\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1$

${{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;}=0$

${{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;\&prime;}=0$

Input:

${\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s={\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1$

${{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;}={\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2$

${{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;\&prime;}=-{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2\&times;{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1$

Input:

${\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s={\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1$

${{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;}={\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2$

${{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;\&prime;}={\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_3-{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2\&times;{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1$

Input:

${\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s={\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1$

${{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;}={\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2$

${{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;\&prime;}={\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_3+{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_3-{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2\&times;{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1$

Input:

${\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s={\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1$

${{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;}={\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_2+{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2$

${{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;\&prime;}={\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_3+{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_3-{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2\&times;{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1-{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_2\&times;{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1$

At last, exist Input:

${\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s={\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_1+{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1---\left(1\right)$

${{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;}={\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_2+{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2-{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_1\&times;{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1---\left(2\right)$

${{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;\&prime;}={\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_3+{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_3-{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2\&times;{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1-{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_2\&times;{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1-{2\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_1\&times;({\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_2+{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2)+{({\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_1\&times;)}^2{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1---\left(3\right)$

Equation (1-3) will be used to decide in the following Example compensating element, Required value.

Example 1: Utilize the PMD of fixing disperisivity quotient element compensation to a specific rank item

By the Electronics Letters (volume 30 of people such as T.Takahashi in 1994, the 348-350 page or leaf)] and people such as F.Roy at Proceeding of Optical Fiber CommunicationsConference (paper TuS4 volume 1 in 1999, the 275-277 page or leaf) a kind of method of Jian Yi compensation single order PMD is: at system's output terminal, adopt a Polarization Controller (PC) and fixing differential group delay element (for example, the polarization maintaining optical fibre of a segment length).By regulating this Polarization Controller, a PMD vector of total system (transmission link+compensator) can be harmonized and the polarization alignment that is transmitted into transmission link forcibly.Thereby the emission polarization is the principal state of polarization (psp) of total system (link+compensator).The fine understanding of the operation of this compensator, and in a large amount of laboratories and practical scene, tested.

As shown in Figure 7, this example has been used the notion scheme (that is to say equation 1-3) of high power time swing element and will have been used the idea of fixed compensation element to extend in order to compensation high-order PMD.This compensator constitutes by being polarized the separated fixing disperisivity quotient element of controller.Mainly, we wish to force the axle r that combine of the emission state aligning of polarization by transmission link and the PMD compensator that is used for each order polarization mode dispersion _n

For example, from equation (1), we wish input polarization

With ${\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s={\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_1+{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1$ Aim at, this means

${a\hat{s}}_{\mathrm{in}}={\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s={\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_1+{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1---\left(4\right)$

Wherein a is a scalar constant.If Be known, and

Size fix, Polarization Controller can make

Direction be adjusted to and meet equation (4).

Similarly from equation (2), we wish with With Aim at, this means

${b\hat{s}}_{\mathrm{in}}={\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s^{\&prime;}={\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_2+{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2-{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_2\&times;{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1---\left(5\right)$

Wherein b is a scalar constant.Here,

With Be known (and fixing), and

Direction can be adjusted to equation (5).

At last, from equation (3), we wish

With Aim at, this means

${c\hat{s}}_{\mathrm{in}}={{\stackrel{\&RightArrow;}{\mathrm{\&tau;}}}_s}^{\&prime;\&prime;}={\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_3+{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_3-{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2\&times;{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1-{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_2\&times;{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1-2{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_1\&times;({\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_2+{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2)+{({\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_1\&times;)}^2{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1---\left(6\right)$

Wherein c is a scalar constant.Here, ${\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_1,{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_2,{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_3,\left|{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1\right|,\left|{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2\right|$ With Be known (and fixing), and Angle can be adjusted to and meet equation (6).

Please note that the higher order term of equation (4) and (5) expression PMD does not enter the condition of low order PMD compensation.The method of this set compensator means: the setting of higher order term does not influence the low order setting that has before performed, and this just makes compensator to realize with comparalive ease and to control.This means: in the actual realization of compensator, be provided with

With

The algorithm of value can be simply by at first regulating

Then regulate

Regulate then

Finish.If the PMD vector information for different orders is directly provided by monitor, this algorithm should not need regulated

(regulating before

With Afterwards) rebound goes to regulate again

Fig. 9 has shown one basic realization in these fixed disperisivity quotient elements.

Figure 10 has shown the vector relations figure that is described by equation (4-6).Note that to each order and defined a plane.Be noted that equally for easy operation, we should select $\left|{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1\right|>\left|{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_1\right|$ (that is: the DGD of single order rotating element should be bigger than the DGD of the maximum of wanting to compensate).Equally, $\left|{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2\right|>|{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_2-{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_1\&times;{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1|$ (that is: the disperisivity quotient of second order compensating element, should be bigger than the second order PMD of the maximum of wanting to compensate), and,

$\left|{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_3\right|>|{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_3-{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2\&times;{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1-{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_2\&times;{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1-2{\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_1\&times;({\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_2+{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_2)+{\left({\stackrel{\&RightArrow;}{\mathrm{\&rho;}}}_1\right)}^2{\stackrel{\&RightArrow;}{\mathrm{\&eta;}}}_1|,$

(that is to say that the disperisivity quotient slope of three rank compensating element,s should be bigger than three rank PMD of the maximum of wanting to compensate)

Be noted that by adding have quadravalence and more the frequency swing of high-order element (that is,

M 〉=4 wherein), the present invention can be extended and be used for compensating the PMD higher than three rank.

Example 2: Utilize the PMD of adjustable disperisivity quotient element compensation to a specific order

Another kind of alternative embodiment of the fixed disperisivity quotient element of describing in 1 as an example, compensating element,

With Can be made into fully adjustable and can be arranged to satisfy equation (4-6).In order to make With Adjustable fully (here, $\stackrel{\&RightArrow;}{{\mathrm{\&eta;}}_n}=k_n{\widehat{\mathrm{\&gamma;}}}_n$ And with the rotation angle of frequency dependence be φ _n(ω ₀+ Δ ω)=k _nΔ ω ⁿ/ n! ), the turning axle of high-order rotating element

(k _n) size must be adjustable.This can utilize the interelement Polarization Controller of adjustable disperisivity quotient of specific order to realize using.Yet,, can realize the optimization of PMD compensation though the embodiment in the embodiment ratio 1 of this selection need more be used for the control signal of compensator.For example, complete adjustable disperisivity quotient element minimizes the undesirable high-order PMD that is produced by the PMD compensator.

For

The differential delay element that can adopt standard for example optics-mechanical delay line (sees that people such as F.Heismann was at Proceedings of European Conference on OpticalCommunication volume 11 in 1998, the 529th page of literary composition), non-linear chirp effect PM Fiber Bragg Grating FBG (seeing people such as S.Lee at Proceddings of Optical Fiber CommunicationsConference in 1999, paper TuS3 literary composition) but or have the PM fiber segment (seeing that people such as D.Sobiski roll up 37 46-48 literary compositions at the Electronics of calendar year 2001 Letters) of switch half-wave plate and full-wave plate.

For Used a kind of adjustable group rate dispersion element, rather than delay element.This adjustable dispersion element can be the optical fiber ripple glug grating (seeing that people such as B.Eggleton is at IEEE Photonics Technology Letters volume 11,854-856 page or leaf literary composition) and an optical circulator of the chirp with grating thermal tuning.Another kind of realize comprising that a virtual image phased array with adjustable dispersion (sees that people such as M.Shirasaki was at Proceedings of European Conference onOptical Communication in 2000, article among the post-deadline paper 2.3), or use the adjustable all-pass filter of toroidal cavity resonator (to see that people such as C.Madsen was at IEEE PhotonicsTechnology Letters in 1999, volume 11, the article on the 1623-1625 page or leaf).Another kind of realization comprises adjustable (adjustable) high-order mode dispersion compensator, as the Proceedings of European Conference on Optical Communication of people such as S.Ramachandran in 2002, what propose among the paperPD2.6 is such.Be noted that: should be noted that the differential group delay of eliminating any of these element.

For

Need adjustable chromatic dispersion gradient element.These elements can realize in tunable bragg gratings that this grating is arrived second order to produce chromatic dispersion gradient by chirp.Can use any element with adjustable dispersion slope.Equally, note eliminating any differential group delay or the disperisivity quotient of these elements.

It is to be noted once more: the element that has quadravalence or a more frequency rotation of high-order by adding (promptly M 〉=4 wherein), the present invention is extensible compensates than the three rank PMD of high-order more.

Now as can be seen, in first aspect, the present invention includes a fibre-optic transmission system (FOTS), this system comprises: one is comprising carrier frequency ω ₀Frequency range in light source; One is used to transmit the Optical Fiber Transmission path of light, and this path has suffered undesirable polarization mode dispersion (PMD); An and polarization mode dispersion compensator that is used to reduce PMD.This compensator comprises a plurality of compensating element,s, and each different compensating element, is configured and is disposed for compensation at ω ₀The rank item that increases one by one of the PMD of place.For example, first compensation of a plurality of compensating element,s is at ω ₀The PMD vector at place Second compensating element, compensation is at ω ₀The PMD vector at place is with respect to the slope of frequency The 3rd compensating element, can compensate PMD with respect to the slope of the frequency speed with frequency change

On the other hand, the present invention also comprises PMD compensator described above.In an advantageous embodiments, each element of PMD compensator comprises: a polarization beam splitter is used for the polarized component beam splitting between two paths with a light beam; A delay or a dispersion element that is positioned on the path wherein; And one be used for polarization combiner that polarized component is reconfigured.As mentioned above, postpone or dispersion element can be that what to fix also can be adjustable, the fixing or adjustable differential delay or the compensating element, of chromatic dispersion are arranged thereby lead fixture.

Proposed the monitoring technique of several PMD of being used for compensators, it can provide the different information of the distortion that causes because of PMD about the PMD of optical fiber or signal.The example of these watch-dogs comprises RF optical spectrum monitor (seeing people such as Takahashi 1994), RF power (was seen people such as H.Bulow 1999, Proceedings of European Conference on Optical Communication volume 2, the 138-139 page or leaf), naked eyes monitoring (seeing people Proceedings ofEuropean in 2000 Conference on Optical Communication such as H.Bulow, volume 3 .209-210 page or leaf), and polarization degree (people such as Roy, 1999).Depend on the information that can obtain from the receiver that is positioned at PMD compensator output and/or PMD detecting device, the parts of foregoing PMD compensator can be adjusted to (forming with fixing or adjustable disperisivity quotient element) by Polarization Controller the different orders of minimizing PMD influence or obtain the optimum performance (for example, minimum the bit error rate) of transmission signals simply.The latter may need shivering of polarizer or adjustable dispersion element tuning.Roll up 1 as people such as F.Buchali at Proceedings of Optical Fiber Communications Conference in 2003, as described in the 262-264 page or leaf, this scheme has been used in the multistage PMD compensator of other type, and may a kind of advantageous scheme for PMD compensator recited above, this PMD compensator can be and is appreciated that the above embodiments only are many a little illustrative embodiment that represents the possible specific embodiment of typical case's application of the present invention.For example, except above-described those, but other rank preface of using compensation parts also, and depend on its application and can find to have superiority.For a person skilled in the art, can make countless other embodiments miscellaneous under spirit of the present invention and the category not breaking away from.

Claims (24)

1. fibre-optic transmission system (FOTS), it comprises:

One is comprising carrier frequency ω ₀Frequency range in work light source;

One is used to transmit the Optical Fiber Transmission path of light, and this path has suffered undesired polarization mode dispersion (PMD); And

One polarization mode dispersion compensator is used to reduce the influence of PMD, and this compensator comprises a plurality of compensating element,s, and each different compensating element, is set in order to compensation at ω ₀Locate the rank item that increase on rank that pursues of PMD.

2. fibre-optic transmission system (FOTS) as claimed in claim 1 is characterized in that: a compensation in a plurality of compensating element,s is at ω ₀The PMD vector at place

Another compensating element, compensation is at ω ₀The PMD of place vector is with respect to the slope of frequency curve

3. transmission system as claimed in claim 2 is characterized in that: another one compensating element, compensation PMD vector is with respect to the slope of the frequency speed with frequency change

4. transmission system as claimed in claim 2 is characterized in that: compensation Compensating element, comprise a differential optical delay line.

5. transmission system as claimed in claim 4 is characterized in that: this differential optical delay line is one section polarization maintaining optical fibre.

6. transmission system as claimed in claim 2 is characterized in that: compensation Compensating element, comprise a differential group velocity dispersion element.

7. transmission system as claimed in claim 6 is characterized in that: be used for compensation

The chromatic dispersion of disperisivity quotient element provide by a chromatic dispersion compensated optical fiber or an optical fiber Bragg (Brag) grating.

8. transmission system as claimed in claim 6 is characterized in that: differential group velocity dispersion element is for having the optical fiber of the certain-length of different chromatic dispersions for two cross polarizations.

9. transmission system as claimed in claim 3 is characterized in that: compensation

Compensating element, comprise a disperisivity quotient slope element.

10. a polarization mode dispersion compensator is used for minimizing and is comprising ω ₀Frequency range in the polarisation of light modal dispersion (PMD) that is transmitted, it is characterized in that: the PMD compensating element, of a plurality of series connection, each compensating element, are set in order to compensation and are expressed as PMD vector about the taylor series expansion of centre frequency

The rank item that increases one by one.

11. polarization mode dispersion compensator as claimed in claim 8 is characterized in that:

An element compensation

Another element compensation And

An other element compensation

Wherein For at ω ₀The place

For At ω ₀The first order derivative at place, For

At ω ₀The second derivative at place.

12. polarization mode dispersion compensator as claimed in claim 11 is characterized in that: compensation

Element comprise a Polarization Controller and one section polarization maintaining optical fibre.

13. polarization mode dispersion compensator as claimed in claim 11 is characterized in that: compensation Element comprise a Polarization Controller and one section optical fiber that has different chromatic dispersions for two orthogonal polarization components.

14. polarization mode dispersion compensator as claimed in claim 11 is characterized in that: each element comprises:

One polarization beam splitter is used for the polarized component beam splitting between two paths with light beam, and this two path has the different chromatic dispersion of specific rank item;

One optical polarization beam combiner is used for polarized component is reconfigured; And

One Polarization Controller, be used for before polarization beam splitter with the rotation of the polarization state of light beam.

15. polarization mode dispersion compensator as claimed in claim 14 is characterized in that: have the element of the chromatic dispersion of a specific order on the path after polarization beam splitter, and on another path, do not have dispersion element.

16. polarization mode dispersion compensator as claimed in claim 14 is characterized in that: the path after the polarization beam splitter each has the element with a specific order chromatic dispersion, and its dispersion values is different.

17. polarization mode dispersion compensator as claimed in claim 14 is characterized in that: the path after the polarization beam splitter each has the element with a specific order chromatic dispersion, and but chromatic dispersion has identical size opposite symbol.

18. polarization mode dispersion compensator as claimed in claim 14 is characterized in that: the element with specific order chromatic dispersion has adjustable chromatic dispersion.

19. polarization mode dispersion compensator as claimed in claim 14 is characterized in that: the element with specific order chromatic dispersion has fixing chromatic dispersion.

20. polarization mode dispersion compensator as claimed in claim 16 is characterized in that: the element with specific order chromatic dispersion has adjustable chromatic dispersion.

21. polarization mode dispersion compensator as claimed in claim 16 is characterized in that: the element with specific order chromatic dispersion has fixing chromatic dispersion.

22. polarization mode dispersion compensator as claimed in claim 17 is characterized in that: the element with specific order chromatic dispersion has adjustable chromatic dispersion.

23. polarization mode dispersion compensator as claimed in claim 17 is characterized in that: the element with specific order chromatic dispersion has fixing chromatic dispersion.

24. polarization mode dispersion compensator as claimed in claim 11 is characterized in that: further comprise one or more additional compensating element,s, be used to compensate one or more rank items that on rank, compare three rank Xiang Genggao of PMD vector.

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